(a) Field of the Invention
The present invention relates to a method of designing a high magnetic field superconducting magnet. More specifically, the present invention relates to the design method of superconducting magnets for generating a high magnetic field with high uniformity for acquiring structural and magnetic stability by respectively arranging positions and forms of coils configuring a superconducting magnet in an optimized method.
(b) Description of the Related Art
A solenoid superconducting magnet is applied to systems that require high uniformity and high magnetic fields in a predetermined space such as a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS), a nuclear magnetic resonance (NMR) instrument, and a magnetic resonance imaging (MRI) instrument. Conventional permanent superconducting magnets for generating high magnetic fields are designed by using the multi-section solenoid scheme with magnetic compensation in which a plurality of solenoids are arranged in the axial direction and spatial positions and geometric forms of coils are optimized so as to offset up to 8- or 12-degree Legendre function terms on required magnetic fields. In this instance, in order to arrange the solenoid coils in an optimized method, a volume including superconducting wires is defined to be a reference so as to reduce the cost of superconducting wires to be used by setting the spatial positions and the geometric shapes of the respective coils as design factors, a first optimization is performed with design information given from the instrument and the superconducting wire as restriction conditions, and a second optimization is performed with an allowable stress as an optimization condition for the purpose of structural stability of the designed coils, thereby acquiring the structural stability.
It is important for the first optimization to establish factors on the initial coil division since the first optimization initially determines division of coils and then optimizes the division, and it frequently fails to provide solutions since multi-variable optimizations cannot satisfy various given conditions. It is easy for the superconducting magnet below 7 Tesla that uses a single main coil without dividing the main coil to establish initial values since restriction conditions and calculation on the initial values are simple. However, the design of a superconducting magnet for acquiring high magnetic fields of more than the 9 Tesla requires division of the main coil, and the establishment of appropriate standards for dividing the coil completely depends on trial and error and designer experience. Therefore, it is needed to develop appropriate standards in order to reduce time loss and acquire system reliability.
The second optimization performs optimization that uses the multi-variable nonlinear optimization scheme by establishing design information provided by the device and the superconducting wire on the reference forms of the volume cost of coils, and establishing the allowable stress to be an additional restriction condition for the purpose of the structural stability of coils. In this instance, since plural partial minimum values can be given due to the characteristics of the multi-variable nonlinear optimization function, selection of a desired solution depends on the designer's experience, and it takes time and effort to check and estimate various results and determine an appropriate optimal solution. Also, the coil is multi-divided as the intensity of the magnetic field to be acquired from the superconducting magnet has a higher field, and hence variables used in the function are added and therefore the restriction conditions are to be additionally established, but additional restriction conditions cannot be established since the currently used restriction conditions are not for the respective divided coils but for the whole coil. Further, since the number of restriction conditions is less, a large number of partial minimum values are problematically provided, and hence it is required to establish restriction conditions that can be suitably added according to division of coils.
In the conventional method for progressing the coil optimization design through the first optimization and the second optimization, structural stability can be achieved by using the allowable stress and the injected current can be reduced to thereby improve temporal stability, but it is more important to acquire magnetic stability related to temporal maintenance in order to more efficiently manage the permanent superconducting magnet.